feat(run-mount): add support for variable expansion

frontend/dockerfile/dockerfile2llb/convert_runmount.go

@@ -20,12 +20,14 @@ func detectRunMount(cmd *command, allDispatchStates *dispatchStates) bool {
 		mounts := instructions.GetMounts(c)
 		sources := make([]*dispatchState, len(mounts))
 		for i, mount := range mounts {
-			if mount.From == "" && mount.Type == instructions.MountTypeCache {
-				mount.From = emptyImageName
-			}
-			from := mount.From
-			if from == "" || mount.Type == instructions.MountTypeTmpfs {
-				continue
+			var from string
+			if mount.From == "" {
+				// this might not be accurate because the type might not have a real source (tmpfs for instance),
+				// but since this is just for creating the sources map it should be ok (we don't want to check the value of
+				// mount.Type because it might be a variable)
+				from = emptyImageName
+			} else {
+				from = mount.From
 			}
 			stn, ok := allDispatchStates.findStateByName(from)
 			if !ok {

frontend/dockerfile/dockerfile_mount_test.go

@@ -20,6 +20,11 @@ var mountTests = []integration.Test{
 	testMountTmpfs,
 	testMountRWCache,
 	testCacheMountDefaultID,
+	testMountEnvVar,
+	testMountArg,
+	testMountEnvAcrossStages,
+	testMountMetaArg,
+	testMountFromError,
 }
 
 func init() {
@@ -221,3 +226,158 @@ RUN --mount=type=cache,target=/mycache [ -f /mycache/foo ]
 	}, nil)
 	require.NoError(t, err)
 }
+
+func testMountEnvVar(t *testing.T, sb integration.Sandbox) {
+	f := getFrontend(t, sb)
+
+	dockerfile := []byte(`
+FROM busybox
+ENV SOME_PATH=/mycache
+RUN --mount=type=cache,target=/mycache touch /mycache/foo
+RUN --mount=type=cache,target=$SOME_PATH [ -f $SOME_PATH/foo ]
+`)
+
+	dir, err := tmpdir(
+		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+	)
+	require.NoError(t, err)
+	defer os.RemoveAll(dir)
+
+	c, err := client.New(context.TODO(), sb.Address())
+	require.NoError(t, err)
+	defer c.Close()
+
+	_, err = f.Solve(context.TODO(), c, client.SolveOpt{
+		LocalDirs: map[string]string{
+			builder.DefaultLocalNameDockerfile: dir,
+			builder.DefaultLocalNameContext:    dir,
+		},
+	}, nil)
+	require.NoError(t, err)
+}
+
+func testMountArg(t *testing.T, sb integration.Sandbox) {
+	f := getFrontend(t, sb)
+
+	dockerfile := []byte(`
+FROM busybox
+ARG MNT_TYPE=cache
+RUN --mount=type=$MNT_TYPE,target=/mycache2 touch /mycache2/foo
+RUN --mount=type=cache,target=/mycache2 [ -f /mycache2/foo ]
+`)
+
+	dir, err := tmpdir(
+		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+	)
+	require.NoError(t, err)
+	defer os.RemoveAll(dir)
+
+	c, err := client.New(context.TODO(), sb.Address())
+	require.NoError(t, err)
+	defer c.Close()
+
+	_, err = f.Solve(context.TODO(), c, client.SolveOpt{
+		LocalDirs: map[string]string{
+			builder.DefaultLocalNameDockerfile: dir,
+			builder.DefaultLocalNameContext:    dir,
+		},
+	}, nil)
+	require.NoError(t, err)
+}
+
+func testMountEnvAcrossStages(t *testing.T, sb integration.Sandbox) {
+	f := getFrontend(t, sb)
+
+	dockerfile := []byte(`
+FROM busybox as stage1
+
+ENV MNT_ID=mycache
+ENV MNT_TYPE2=cache
+RUN --mount=type=cache,id=mycache,target=/abcabc touch /abcabc/foo
+RUN --mount=type=$MNT_TYPE2,id=$MNT_ID,target=/cbacba [ -f /cbacba/foo ]
+
+FROM stage1
+RUN --mount=type=$MNT_TYPE2,id=$MNT_ID,target=/whatever [ -f /whatever/foo ]
+`)
+
+	dir, err := tmpdir(
+		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+	)
+	require.NoError(t, err)
+	defer os.RemoveAll(dir)
+
+	c, err := client.New(context.TODO(), sb.Address())
+	require.NoError(t, err)
+	defer c.Close()
+
+	_, err = f.Solve(context.TODO(), c, client.SolveOpt{
+		LocalDirs: map[string]string{
+			builder.DefaultLocalNameDockerfile: dir,
+			builder.DefaultLocalNameContext:    dir,
+		},
+	}, nil)
+	require.NoError(t, err)
+}
+
+func testMountMetaArg(t *testing.T, sb integration.Sandbox) {
+	f := getFrontend(t, sb)
+
+	dockerfile := []byte(`
+ARG META_PATH=/tmp/meta
+
+FROM busybox
+ARG META_PATH
+RUN --mount=type=cache,id=mycache,target=/tmp/meta touch /tmp/meta/foo
+RUN --mount=type=cache,id=mycache,target=$META_PATH [ -f /tmp/meta/foo ]
+`)
+
+	dir, err := tmpdir(
+		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+	)
+	require.NoError(t, err)
+	defer os.RemoveAll(dir)
+
+	c, err := client.New(context.TODO(), sb.Address())
+	require.NoError(t, err)
+	defer c.Close()
+
+	_, err = f.Solve(context.TODO(), c, client.SolveOpt{
+		LocalDirs: map[string]string{
+			builder.DefaultLocalNameDockerfile: dir,
+			builder.DefaultLocalNameContext:    dir,
+		},
+	}, nil)
+	require.NoError(t, err)
+}
+
+func testMountFromError(t *testing.T, sb integration.Sandbox) {
+	f := getFrontend(t, sb)
+
+	dockerfile := []byte(`
+FROM busybox as test
+RUN touch /tmp/test
+
+FROM busybox
+ENV ttt=test
+RUN --mount=from=$ttt,type=cache,target=/tmp ls
+`)
+
+	dir, err := tmpdir(
+		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+	)
+	require.NoError(t, err)
+	defer os.RemoveAll(dir)
+
+	c, err := client.New(context.TODO(), sb.Address())
+	require.NoError(t, err)
+	defer c.Close()
+
+	_, err = f.Solve(context.TODO(), c, client.SolveOpt{
+		LocalDirs: map[string]string{
+			builder.DefaultLocalNameDockerfile: dir,
+			builder.DefaultLocalNameContext:    dir,
+		},
+	}, nil)
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "'from' doesn't support variable expansion, define alias stage instead")
+}

frontend/dockerfile/instructions/commands.go

@@ -272,6 +272,13 @@ type RunCommand struct {
 	FlagsUsed []string
 }
 
+func (c *RunCommand) Expand(expander SingleWordExpander) error {
+	if err := setMountState(c, expander); err != nil {
+		return err
+	}
+	return nil
+}
+
 // CmdCommand : CMD foo
 //
 // Set the default command to run in the container (which may be empty).

frontend/dockerfile/instructions/commands_runmount.go

@@ -2,6 +2,7 @@ package instructions
 
 import (
 	"encoding/csv"
+	"regexp"
 	"strconv"
 	"strings"
 
@@ -64,13 +65,17 @@ func runMountPreHook(cmd *RunCommand, req parseRequest) error {
 }
 
 func runMountPostHook(cmd *RunCommand, req parseRequest) error {
+	return setMountState(cmd, nil)
+}
+
+func setMountState(cmd *RunCommand, expander SingleWordExpander) error {
 	st := getMountState(cmd)
 	if st == nil {
 		return errors.Errorf("no mount state")
 	}
 	var mounts []*Mount
 	for _, str := range st.flag.StringValues {
-		m, err := parseMount(str)
+		m, err := parseMount(str, expander)
 		if err != nil {
 			return err
 		}
@@ -111,7 +116,7 @@ type Mount struct {
 	GID          *uint64
 }
 
-func parseMount(value string) (*Mount, error) {
+func parseMount(value string, expander SingleWordExpander) (*Mount, error) {
 	csvReader := csv.NewReader(strings.NewReader(value))
 	fields, err := csvReader.Read()
 	if err != nil {
@@ -151,6 +156,23 @@ func parseMount(value string) (*Mount, error) {
 		}
 
 		value := parts[1]
+		// check for potential variable
+		if expander != nil {
+			processed, err := expander(value)
+			if err != nil {
+				return nil, err
+			}
+			value = processed
+		} else if key == "from" {
+			if matched, err := regexp.MatchString(`\$.`, value); err != nil { //nolint
+				return nil, err
+			} else if matched {
+				return nil, errors.Errorf("'%s' doesn't support variable expansion, define alias stage instead", key)
+			}
+		} else {
+			// if we don't have an expander, defer evaluation to later
+			continue
+		}
 		switch key {
 		case "type":
 			if !isValidMountType(strings.ToLower(value)) {